Dynamic Sea Level Variability Due to Seasonal River Discharge: A Preliminary Global Ocean Model Study

Abstract To determine the possible importance of ENSO events along the coast of South Australia, an exploratory analysis is made of meteorological and oceanographic data and output from a global ocean model. Long time series of coastal sea level and wind stress are used to show that while upwelling favorable winds have been more persistent since 1982, ENSO events (i) are largely driven by signals from the west Pacific Ocean shelf/slope waveguide and not local meteorological conditions, (ii) can account for 10-cm changes in sea level, and (iii) together with wind stress, explain 62% of the variance of annual-averaged sea level. Thus, both local winds and remote forcing from the west Pacific are likely important to the low-frequency shelf edge circulation. Evidence also suggests that, since 1983, wintertime downwelling during the onset of an El Niño is reduced and the following summertime upwelling is enhanced. In situ data show that during the 1998 and 2003 El Niño events anomalously cold (10.5°–11.5°C) water is found at depths of 60–120 m and is more than two standard deviations cooler than the mean. A regression showed that averaged sea level can provide a statistically significant proxy for these subsurface temperature changes and indicates a 2.2°C decrease in temperature for the 10-cm decrease in sea level that was driven by the 1998 El Niño event. Limited current- meter observations, long sea level records, and output from a global ocean model were also examined and provide support for the hypothesis that El Niño events substantially reduce wintertime (but not summertime) shelf-edge currents. Further research to confirm this asymmetric response and its cause is required.

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Deep learning of dynamic sea-level variability to investigate the relationship with the floods in Gothenburg

10.21203/rs.3.rs-422515/v1 ◽

2021 ◽

Author(s):

Omid Memarian Sorkhabi

Keyword(s):

Deep Learning ◽

Wind Speed ◽

Sea Level Rise ◽

Sea Level ◽

Sea Surface ◽

Sea Level Variability ◽

Annual Increase ◽

The Relationship ◽

Dynamic Sea Level ◽

And Sea Level

Abstract It is important to study the relationship between floods and sea-level rise due to climate change. In this research, dynamic sea-level variability with deep learning has been investigated. In this research sea surface temperature (SST) from MODIS, wind speed, precipitation and sea-level rise from satellite altimetry investigated for dynamic sea-level variability. An annual increase of 0.1 ° C SST is observed around the Gutenberg coast. Also in the middle of the North Sea, an annual increase of about 0.2 ° C is evident. The annual sea surface height (SSH) trend is 3 mm on the Gothenburg coast. We have a strong positive spatial correlation of SST and SSH near the Gothenburg coast. In the next step dynamic sea-level variability is predicted with long short time memory. Root mean square error of wind speed, precipitation, and mean sea-level forecasts are 0.84 m/s, 48 mm and 2.4 mm. The annual trends resulting from 5-year periods, show a significant increase from 28 mm to 46 mm per year in the last 5 year periods. The rate of increase has doubled. The wavelet can be useful for detecting dynamic sea-level variability.

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The coherence of small island sea-level with the wider ocean: a model study

Ocean Science Discussions ◽

10.5194/osd-9-3049-2012 ◽

2012 ◽

Vol 9 (5) ◽

pp. 3049-3070

Author(s):

Joanne Williams ◽

Christopher W. Hughes

Keyword(s):

Sea Level ◽

Tide Gauge ◽

Deep Ocean ◽

Ocean Model ◽

Small Island ◽

Poor Agreement ◽

Model Study ◽

Tide Gauge Measurements ◽

The Relationship ◽

Good Agreement

Abstract. Studies comparing tide gauge measurements with sea level from nearby satellite altimetry have shown good agreement for some islands, and poor agreement for others, though no explanation has been offered. Using the 1/12° OCCAM ocean model, we investigate the relationship between sea level at small, open-ocean islands, and offshore sea level. For every such island or seamount in the model, we compare the shallow-water sea level with the steric and bottom pressure variability in a neighboring ring of deep water. We find a latitude-dependent range of frequencies for which off-shore sea level is poorly correlated with island sea level. This poor coherence occurs in a spectral region for which steric signals dominate, but are unable to propagate as baroclinic Rossby waves. This mode of decoupling does not arise because of island topography, as the same decoupling is seen between deep ocean points and surrounding rings.

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Atmospherically forced sea-level variability in western Hudson Bay, Canada

Ocean Science ◽

10.5194/os-17-1367-2021 ◽

2021 ◽

Vol 17 (5) ◽

pp. 1367-1384

Author(s):

Igor A. Dmitrenko ◽

Denis L. Volkov ◽

Tricia A. Stadnyk ◽

Andrew Tefs ◽

David G. Babb ◽

...

Keyword(s):

Sea Ice ◽

Sea Level ◽

River Discharge ◽

Seasonal Cycle ◽

Storm Surges ◽

Wind Forcing ◽

Hudson Bay ◽

Sea Level Variability ◽

Gauge Data ◽

Western Hudson Bay

Abstract. In recent years, significant trends toward earlier breakup and later freeze-up of sea ice in Hudson Bay have led to a considerable increase in shipping activity through the Port of Churchill, which is located in western Hudson Bay and is the only deep-water ocean port in the province of Manitoba. Therefore, understanding sea-level variability at the port is an urgent issue crucial for safe navigation and coastal infrastructure. Using tidal gauge data from the port along with an atmospheric reanalysis and Churchill River discharge, we assess environmental factors impacting synoptic to seasonal variability of sea level at Churchill. An atmospheric vorticity index used to describe the wind forcing was found to correlate with sea level at Churchill. Statistical analyses show that, in contrast to earlier studies, local discharge from the Churchill River can only explain up to 5 % of the sea-level variability. The cyclonic wind forcing contributes from 22 % during the ice-covered winter–spring season to 30 % during the ice-free summer–fall season due to cyclone-induced storm surges generated along the coast. Multiple regression analysis revealed that wind forcing and local river discharge combined can explain up to 32 % of the sea-level variability at Churchill. Our analysis further revealed that the seasonal cycle of sea level at Churchill appears to be impacted by the seasonal cycle in atmospheric circulation rather than by the seasonal cycle in local discharge from the Churchill River, particularly post-construction of the Churchill River diversion in 1977. Sea level at Churchill shows positive anomalies for September–November compared to June–August. This seasonal difference was also revealed for the entire Hudson Bay coast using satellite-derived sea-level altimetry. This anomaly was associated with enhanced cyclonic atmospheric circulation during fall, reaching a maximum in November, which forced storm surges along the coast. Complete sea-ice cover during winter impedes momentum transfer from wind stress to the water column, reducing the impact of wind forcing on sea-level variability. Expanding our observations to the bay-wide scale, we confirmed the process of wind-driven sea-level variability with (i) tidal-gauge data from eastern Hudson Bay and (ii) satellite altimetry measurements. Ultimately, we find that cyclonic winds generate sea-level rise along the western and eastern coasts of Hudson Bay at the synoptic and seasonal timescales, suggesting an amplification of the bay-wide cyclonic geostrophic circulation in fall (October–November), when cyclonic vorticity is enhanced, and Hudson Bay is ice-free.

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The sensitivity of a global ocean model to wind forcing: A test using sea level and wind observations from satellites and operational wind analysis

Geophysical Research Letters ◽

10.1029/97gl01532 ◽

1997 ◽

Vol 24 (14) ◽

pp. 1783-1786 ◽

Cited By ~ 9

Author(s):

Lee-Lueng Fu ◽

Yi Chao

Keyword(s):

Sea Level ◽

Ocean Model ◽

Wind Forcing ◽

Global Ocean ◽

Wind Analysis

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Sea Level Variability around Japan during the Twentieth Century Simulated by a Regional Ocean Model

Journal of Climate ◽

10.1175/jcli-d-16-0497.1 ◽

2017 ◽

Vol 30 (14) ◽

pp. 5585-5595 ◽

Cited By ~ 4

Author(s):

Yoshi N. Sasaki ◽

Ryosuke Washizu ◽

Tamaki Yasuda ◽

Shoshiro Minobe

Keyword(s):

Sea Level Rise ◽

Sea Level ◽

Ocean Model ◽

Freshwater Flux ◽

Wind Stress Curl ◽

Sea Level Variability ◽

The North ◽

Japanese Coast ◽

Regional Ocean Model ◽

Regional Sea Level

Sea level variability around Japan from 1906 to 2010 is examined using a regional ocean model, along with observational data and the CMIP5 historical simulations. The regional model reproduces observed interdecadal sea level variability, for example, high sea level around 1950, low sea level in the 1970s, and sea level rise during the most recent three decades, along the Japanese coast. Sensitivity runs reveal that the high sea level around 1950 was induced by the wind stress curl changes over the North Pacific, characterized by a weakening of the Aleutian low. In contrast, the recent sea level rise is primarily caused by heat and freshwater flux forcings. That the wind-induced sea level rise along the Japanese coast around 1950 is as large as the recent sea level rise highlights the importance of natural variability in understanding regional sea level change on interdecadal time scales.

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On the Drivers and Predictability of Seasonal-to-Interannual Variations in Regional Sea Level

Journal of Climate ◽

10.1175/jcli-d-15-0886.1 ◽

2016 ◽

Vol 29 (21) ◽

pp. 7565-7585 ◽

Cited By ~ 22

Author(s):

C. D. Roberts ◽

D. Calvert ◽

N. Dunstone ◽

L. Hermanson ◽

M. D. Palmer ◽

...

Keyword(s):

Climate Variability ◽

Sea Level ◽

Time Scales ◽

Large Scale ◽

Meridional Overturning Circulation ◽

Wind Forcing ◽

Thermocline Depth ◽

Sea Level Variability ◽

Modes Of Climate Variability ◽

Dynamic Sea Level

Abstract Observations and eddy-permitting ocean model simulations are used to evaluate the drivers of sea level variability associated with 15 modes of climate variability covering the Atlantic, Pacific, Indian, and Southern Oceans. Sea level signals are decomposed into barotropic, steric, and inverted barometer contributions. Forcings are decomposed into surface winds, buoyancy fluxes, and Ekman pumping. Seasonal-to-interannual sea level variability in the low latitudes is governed almost entirely by the thermosteric response to wind forcing associated with tropical modes of climate variability. In the extratropics, changes to dynamic sea level associated with atmospheric modes of variability include a substantial barotropic response to wind forcing, particularly over the continental shelf seas. However, wind-driven steric changes are also important in some locations. On interannual time scales, wind-forced steric changes dominate, although heat and freshwater fluxes are important in the northwest Atlantic, where low-frequency sea level variations are associated with changes in the Atlantic meridional overturning circulation. Using the version 3 of the Met Office Decadal Prediction System (DePreSys3), the predictability of large-scale dynamic sea level anomalies on seasonal-to-interannual time scales is evaluated. For the first year of the hindcast simulations, DePreSys3 exhibits skill exceeding persistence over large regions of the Pacific, Atlantic, and Indian Oceans. Skill is particularly high in the tropical Indo-Pacific because of the accurate initialization and propagation of thermocline depth anomalies associated with baroclinic adjustments to remote wind forcing. Skill in the extratropics is hindered by the limited predictability of wind anomalies associated with modes of atmospheric variability that dominate local and/or barotropic responses.

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Estimation of the Atlantic sea-level response to atmospheric pressure using ERS-2 altimeter data and a global ocean model

10.1117/12.452744 ◽

2002 ◽

Author(s):

Jesus Gomez-Enri ◽

Pilar Villares ◽

Miguel Bruno ◽

Jerome Benveniste

Keyword(s):

Sea Level ◽

Atmospheric Pressure ◽

Ocean Model ◽

Global Ocean ◽

Altimeter Data

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Atmospherically-forced sea-level variability in western Hudson Bay, Canada

10.5194/os-2021-50 ◽

2021 ◽

Author(s):

Igor Dmitrenko ◽

Denis Volkov ◽

Tricia Stadnyk ◽

Andrew Tefs ◽

David Babb ◽

...

Keyword(s):

Sea Ice ◽

Sea Level ◽

Atmospheric Circulation ◽

River Discharge ◽

Seasonal Cycle ◽

Wind Forcing ◽

Hudson Bay ◽

Sea Level Variability ◽

Gauge Data ◽

Western Hudson Bay

Abstract. In recent years, significant trends toward earlier breakup and later freeze‐up of sea-ice in Hudson Bay have led to a considerable increase in shipping activity through the Port of Churchill, which is located in western Hudson Bay and is the only deep-water ocean port in the province of Manitoba. Therefore, understanding sea level variability at the Port is an urgent issue crucial for safe navigation and coastal infrastructure. Using tidal gauge data from the Port along with an atmospheric reanalysis and Churchill River discharge, we assess environmental factors impacting synoptic to seasonal variability of sea-level at Churchill. An atmospheric vorticity index used to describe the wind forcing was found to correlate with sea level at Churchill. Statistical analyses show that, in contrast to earlier studies, local discharge from the Churchill River can only explain up to 5 % of the sea level variability. The cyclonic wind forcing contributes from 22 % during the ice-covered winter-spring season to 30 % during the ice-free summer-fall season due to cyclone-induced storm surge generated along the coast. Multiple regression analysis revealed that wind forcing and local river discharge combined can explain up to 32 % of the sea level variability at Churchill. Our analysis further revealed that the seasonal cycle of sea level at Churchill appears to be impacted by the seasonal cycle in atmospheric circulation rather than by the seasonal cycle in local discharge from the Churchill River, particularly post-construction of the Churchill River diversion in 1977. Sea level at Churchill shows positive anomalies for September–November compared to June–August. This seasonal difference was also revealed for the entire Hudson Bay coast using satellite-derived sea level altimetry. This anomaly was associated with enhanced cyclonic atmospheric circulation during fall, reaching a maximum in November, which forced storm surges along the coast. Complete sea-ice cover during winter impedes momentum transfer from wind stress to the water column, reducing the impact of wind forcing on sea level variability. Expanding our observations to the bay-wide scale, we confirmed the process of wind-driven sea-level variability with (i) tidal-gauge data from eastern Hudson Bay and (ii) satellite altimetry measurements. Ultimately, we find that cyclonic winds generate sea level rise along the western and eastern coasts of Hudson Bay at the synoptic and seasonal time scales, suggesting an amplification of the bay-wide cyclonic geostrophic circulation in fall (October–November), when cyclonic vorticity is enhanced, and Hudson Bay is ice-free.

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